Reactivation of nitration reaction vessels



Patented Apr. 1, 1941 2,236,905 REACTIVATION V1; NITBATION REACTION SSELS Edward B. Hodge, Terre Hautc, Ind and Lloyd G:

Swallen, Pekin, IlL, assignors to Commercial Solvents Corporation, Terre 'Haute, Ind., a (501'? poration of Delaware No Drawing. Application May 6, 1939, Serial No. 272,152

11 Claims.

Our invention relates to the production of nltrohydrocarbons. More specifically, our invention relates to an improvement in the production of nitrohydrocarbons by the direct vapor phase nitration of saturated hydrocarbons.

The direct vapor phase nitration of saturated hydrocarbons is described in U. S. Patent No. 1,967,667 of H. B. Hass et al., U. S. Patent No. 2,071,122 of H. B. Hass et al.. and in co-pending application Serial No. 98,634 of H. B. Hass et 9.1. According to this process saturated hydrocarbons and nitric acid, or nitrogen dioxid are contacted in a reaction vessel maintained at a sufllciently high temperature to insure vapor phase conditions at the pressure employed. Although this reaction gives satisfactory initial yields and conversions, we have found that there is a tendency for these yields and conversions to drop 011' after continued operation. This effect is similar to the deterioration or poisoning of a catalyst in a catalytic reaction, but as there is no catalyst employed in the present case the explanation of this phenomenon is not clear. It appears that after a certain period of operation the interior walls of the reaction vessel acquire reaction-in-- hibiting characteristics. This result seems to be due to the fact that a material which catalyzes undesired reactions tends to build up in the system. This theory is supported by the fact that the phenomenon is encountered to diflerent degrees in reaction vessels of different compositions, and also by the fact that the nitric acid is destroyed in the reaction even when the yield of nitrohydrocarbon has markedly dropped off. It should be understood, however, that our invention is not to be construed as limited to any theoretlcal explanation of the above described phenomenon. Irrespective of the true explanation of this reaction-inhibiting phenomenon, we will refer to it herein for convenience as "deactivation of the reaction vessel."

We have found that reactors made of copper aluminum, or iron, or of the ferrous alloys such as stainless iron or stainless steel,'which are particularly suited for the construction of such apparatus, deactivate relatively easily, and that this' deactivation is accelerated by contact of any liquid nitric acid with the interior surfaces of the reaction vessel. Although these reaction vessels become deactivated relatively slowly during use, we have found that they' may be rapidly deactivated by treatment of the interior surfaces of the vessel with liquid nitric acid. when the reaction vessel has been deactivated either by continued use or by accelerated treatment with liquid nitric acid, it is unsuitable for further economic operation of the nitration reaction. All prior attempts to reactivate the vessel when in this condition, as for example, by thorough washing with water or by heat treatment, have failed.

We have now found that the deactivated react-ion vessels may be satisfactorily reactivated by treatment with a compound of a metal of the alkali or alkaline earth groups. Among the various compounds of these metals, the reactivating powers of the individual compounds will be found to differ to a' considerable extent. Thus, in comparing various compounds of lithium, sodium, potassium, calcium, strontium, and barium, we have found that the compounds of the alkaline earth metals tend to be less active than the compounds of the alkali metals. Similarly, we have found that the salts which are substantially water-insoluble, i. e., soluble in water at 20 C. to the extent of less than 1. g. per ml. of water,

are generally less active than the more soluble salts or the free bases, 1. e., the oxides or hydroxides. We prefer, therefore, to employ the bases and the substantially water-soluble salts of the alkali and alkaline earth metals, and especially the water-soluble alkali metal compounds; but it is to be understood that our invention is not to be limited to the use of these materials. We have secured positive reactivation of deacti- -vated reaction vessels with a very large number of diflerent alkali metal and alkaline earth metal compounds, and we believe all of the compounds of these metals to be operative if employed under suitable reactivating conditions.

In carrying out our invention it is necessary merely to treat the interior surfaces of the reaction vessel with a compound of the type specifled above, suitably in the form of an aqueous solution or suspension. When the reaction vessel becomes deactivated it should preferably be thoroughly washed with water and filled with a solution of the desired reactivating agent. The concentration of the solution of reactivating agent, and the time of treatment, may be varied within relatively wide limits, but we prefer in most cases to utilize a concentration of at least 1 g. per 100 mL, and preferably 10 to 30 g. per 100 ml.', and to allow the solution to remain in the vessel for a period of 5 to 10 minutes. In the case of relatively may suitably be employed. After standing for the required time the. solution or suspen sion is drained from the vessel, which is then subjected to a heat treatment to complete the reactivation. The reactivating agent adhering to the walls of the vessel apparently undergoes some reaction during the heat treatment, since removal of all the reactivatlng agent by thorough washing prior to heating results in very much diminished reactivating effect.

The heat treatment necessary to complete the reactivation depends to some extent upon the activity of the particular reactivating agent used, less heat treatment generally being required for the more active reactivating agents thanfor the less active agents. A temperature in excess of 100? C., is usually required even for the most active reactivating agents, and less active compounds may require temperatures very much higher. We prefer to employ temperatures at least as high as 200 C., and we have successfully reactivated at temperatures as high as 900 C., or even higher. The more active compounds will reactivate successfully within the range 250- 600 C. Since this constitutes a useful temperature range for the nitration reaction, the reactivation may be completed, after treating with the solution of the reactivating agent, simply by placing the vessel back in operation in the nitration reaction. From the standpoint of simplicity of operation, we prefer to utilize this procedure.

If a separate heat treatment is utilized, rather than relying upon the reaction temperature of the nitratibn reaction to complete the reactivation, the vessel may be washed, if desired, after the heat treatment, and before use in the nitration reaction, This procedure is unnecessary, however, and we generally prefer to employ the vessel directly, without further washing. In the absence of such washing, incomplete reactivation due to insuificient heat treatment will tend to be overcome by the additional heating encountered during use in the nitration reaction. In the usual operation of our process, therefore, it is unnecessary to consider the time factor for the heat treatment. If, however, a separate heat treatment is employed, and the vessel is then washed prior to use, it becomes necessary to ensure a minimum duration of the heat treatment suflicient to effect reactivation. This time will differ with the temperature used, and with the activity of the reactivating agent. In general, we prefer to maintain the vessel at the reactivating temperature for at least 5 minutes, and preferably for -60 minutes.' In any partlcularcase, however, preliminary experiments will indicate the minimum time necessary for optimum reactivation at the temperature involved.

Our invention will now be illustrated by specific examples illustrating the reactivating eiiect of various compounds of the group specified above.

Example I Stainless iron reaction tubes of 80 ml. capacity were deactivated by filling with 8 N nitric acid, and

allowing this to remain for a few minutes to secure a degree of deactivation suflicient to reduce the yield of nitrohydrocarbons to 0-1.0 milliliters per hour under the reaction conditions utilized for the test. The reaction tubes were then blown out with air, replaced in the apparatus, and test runs made to determine the yield of nitrohydrocarbons per hour with the deactivated tubes. The reactants were propane and nitric acid, and the following reaction conditions were maintained:

Pressure 30 lbs. gage Nitric acid feed rate (13.5 N)- 960 ml. per hour Propane feed rate 950 l. per hour (760 mm., 25 C.) Reaction temperature 430-45 C. Vaporizer temperature 220-30 C.

After-determining the yields with the deactivated tubes, the tubes were reactivated by washing with water and treating with solutions of various reactivating agents After reactivation further test runs were made to determine the yield of nitrohydrocarbons with the reactivated tubes. The same reaction conditions were maintained as Yield of nitro- Yield of nitrohydrocarbons hydrocarbons beiore reactialter reactivation vation Reactivlting agent Example II The procedure of Example I was followed with the exception that the reaction tubes were deactivated only to a point corresponding to yields of nitrolnrdrocarbons of approximately -90 milliliters per hour. The results secured are given in the table below:

Yield oi n ltro- Yield of nitro- 1.] ul IL I Reactivltmg agent m 32 1" vation vltion sessese The above examples illustrate that satisfactory reactivation may be secured irrespective of the stage of deactivation of the reaction vessel. It is thus possible to reactivate at any time when the yield drops-sufliciently to warrant stopping the process for the period necessary to reactivate. In view of the fact that the reactivation procedure is extremely simple, and a very short time is required, it will usually be found to be desirable tc reactivate when the degree of deactivation secured is even less than that indicated in Example II.

It is to be understood, of course, that the above examples are not to be construed as limiting the scope of our invention. As has previously been pointed out, other compounds of thealkali or alkaline earth metals may be utilized in place of the particular compounds specified above. For example, we have succeeded in reactivating deactivated reaction vessels with each of the following compounds: lithium hydroxide, sodium chloride, sodium sulfate, sodium cyanide, sodium silicofluoride, sodium sulfide, sodium sulflte, sodium bisulfite, sodium aminosalicylate, sodium methoxide, sodium oxalate, sodium citrate, sodium glyceroxide, sodium butyl phthalate, sodium ethyl phosphate,' sodium benzenesulfonate, methyl orange (sodium salt), potassium hydroxide, potassium sulfate, potassium bisulfate, potassium sulfocyanide, potassium phthalimide, potassium uranate, calcium hydroxide, calcium arsenate, strontium chloride, strontium sulfate, barium chloride and barium phosphate.

The vast majority of the alkali and alkaline earth metal compounds which we have tried (over have given positive results ln reactivating deactivated reaction vessels. In the cases of calcium sulfate, calcium carbonate and barium carbonate, however, we have failed to secure positive reactivation under any conditions attempted, even, in some cases, when heating the treated vessel to red heat. It is possible, however, that with even more drastic heat treatment, these compounds likewise would be effective. In any event, in view of the large number of operative compounds previously mentioned, and an even larger number of obvious equivalents of such compounds, it will'be unnecessary for one skilled in the art to attempt to employ the few apparently inactive compounds, such as the specific alkaline'earth metal sulfates and carbonates mentioned above.

It will also be obvious to those skilled in the art that the procedure described above may be occur to one skilled in the art, are included within the scope of our invention.

This application is a continuation-in-part of our application, Ser. No. 126,640, filed February 19, 1937.

Our invention now having been described, what we claim is:

1. The process of reactivating a reaction vessel which has become deactivated during the vapor phase nitration of saturated hydrocarbons therein, which comprises treating the interior surfaces of the deactivated reaction vessel at a temperature above 100 C. with an agent selected from the group consisting of alkali metal and alkaline earth metal compounds which are active to decrease the reaction-inhibiting characteristics of the deactivated vessel walls.

2. The process of reactivating a reaction vessel which has become deactivated during the vapor phase nitration of saturated hydrocarbons therein, which comprises treating the interior surfaces of the deactivated vessel, at a temperature of 200-900 C., with an alkali metal compound which is active to decrease the reactioninhibiting characteristics of the deactivated vessel walls.

3. The process of reactivating a reaction vessel which has become deactivated during the vapor phase nitration of saturated hydrocarbons therein, which comprises treating the interior suriacesof the deactivated vessel, at a temperature of 200-900 -C., with an alkaline earth metal compound which is active to decrease the reaction-inhibiting characteristics of the deactivated vessel walls.

4. The process of reactivating a reaction vessel which has become deactivated during the vapor phase nitration of saturated hydrocarbons phase nitration of therein, which comprises reactivating the reaction vessel by treating the interior surfaces thereof at a temperature above 100 C., with a compound selected from the group consisting of 5 the bases and the substantially water-soluble salts of the alkali metals and the alkaline earth metals.

5. The process of reactivating a reaction vessel which has become deactivated during the vapor saturated hydrocarbons therein, which comprises reactivating the reaction vessel by treating the interior surfaces thereof at a temperature of 200 to 900 C. with a substantially water-soluble compound of an alkali metal.

6. The process of reactivating a reaction vessel which has become deactivated during the vapor phase nitration of saturated hydrocarbons therein, which comprises reactivating the reaction vessel by treating the interior surfaces thereof at a temperature of 200 to 900 C. with a substantially water-soluble compound of an alkaline earth metal.

7. The process of reactivating -a reaction vessel which has become deactivated during the vapor phase nitration of saturated hydrocarbons therein, which comprises treating the interior surfaces of the deactivated vessel, at a temperature of 250-600 C., with a substantially watersoluble sodium compound.

8. The process of reactivating a reaction vessel which has become deactivated during the vapor phase nitration of saturated hydrocarbons therein, which comprises treating the interior surfaces of the deactivated vessel, at a temperaphase nitration of saturated hydrocarbons therein, which comprises reactivating the reaction vessel by treating the interior surfaces thereof, at a temperature of 250-600 C., with an alkali metal hydroxide.

10. The process of reactivating a reaction vessel which has become deactivated during the vapor phase nitration of saturated hydrocarbons therein, which comprises reactivating the reaction vessel by treating the interior surfaces thereof, at a temperature of 250-600" C., with sodium hydroxide.

11. The process of reactivating a reaction vessel which has become deactivated during the vapor phase nitration of saturated hydrocarbons therein, which comprises reactivating the reaction vessel by treating the interior surfaces thereof, at a temperature of 250-600 C., with otassium hydroxide.

EDWARD B. HODGE.

LLOYD C. SWALLEN. 

